Low solar factor (SF) and solar heat gain coefficient (SHGC) values are desired in some window applications, particularly in warm weather climates. Solar factor (SF), calculated in accordance with EN standard 410, relates to a ratio between the total energy entering a room or the like through a glazing and the incident solar energy. Thus, it will be appreciated that lower SF values are indicative of good solar protection against undesirable heating of rooms or the like protected by windows/glazings. A low SF value is indicative of a coated article (e.g., IG window unit) that is capable of keeping a room fairly cool in summertime months during hot ambient conditions. Thus, low SF values are sometimes desirable in hot environments. High light-to-solar gain (LSG) values are also desirable. LSG is calculated as Tvis/SHGC. The higher the LSG value, the more visible light that is transmitted and the less amount of heat that is transmitted by the coated article. While low SF and SHGC values, and high LSG values, are sometimes desirable for coated articles such as IG window units and/or monolithic windows, the achievement of such values may come at the expense of sacrificing coloration and/or reflectivity values. In particular, conventional attempts to achieve low SF and SHGC values have often resulted in undesirably high visible reflectance value(s) and/or undesirable visible coloration of the coating. Thus, conventional low-E coatings designed for monolithic window applications typically cannot be used to provide low visible transmission (e.g., 15-36%), low SHGC performance absent the use of deeply tinted glass substrates. It is often desirable, but difficult, to achieve a combination of acceptable visible transmission (TY or Tvis), desirable reflective coloration (e.g., desirable a* and b* reflective color values), low SF, low SHGC, and high LSG for a coated article in window applications, especially if it desired to use a glass substrate that is not deeply tinted.
SF (G-Factor; EN410-673 2011) and SHGC (NFRC-2001) values are calculated from the full spectrum (Tvis, Rg and Rf) and are typically measured with a spectrophotometer such as a Perkin Elmer 1050. The SF measurements are done on monolithic coated glass, and the calculated values can be applied to monolithic, IG and laminated applications.
Certain known solar control coatings use NbN, NbZr, or NbZrN as IR reflecting layers. For instance, see U.S. Patent Document 2012/0177899 and U.S. Pat. No. 8,286,395. However, the instant inventors have surprisingly found that solar control coatings that use solely these materials NbN, NbZr, or NbZrN for IR reflecting layers are lacking in terms of normal emissivity (En) for a given IR reflecting layer(s) thickness. For a given IR reflecting layer(s) thickness, the instant inventors have found that such coatings have undesirably high normal emittance (En) values, undesirably high SHGC values; and undesirably low LSG values.
Solar control coatings in U.S. Patent Document 2012/0177899 (incorporated herein by reference) are disclosed having a layer stack of glass/Si3N4/NiCr/Si3N4/NiCr/Si3N4 where the NiCr layer may be nitrided. While layer stacks of U.S. Patent Document 2012/0177899 provide reasonable solar control and are overall good coatings, they are lacking in certain respects. For instance, the glass side visible reflectance values (RGY) in Examples 1, 4 and 5 are 36%, 36.87%, and 15.82%, respectively. Examples 1 and 4 in US '899 are undesirable because the glass side visible reflectance (RGY) values are too high at 36% and 36.87%, respectively, and because the glass side reflective a* values are too negative at −17.8 and −15.95, respectively. And when RGY is reduced down to 15.82% in Example 5, this results in the glass side reflective a* color value in Example 5 becoming rather red with a value of +2.22. While certain example embodiments of the instant invention may have red reflective coloration in certain instances, other example embodiments of this invention have been designed to achieve a combination of desirable visible reflectance values and coloration which is either not red or not too red.
It would be desirable according to example embodiments of this invention for a coating to be designed so as to have a combination of acceptable visible transmission (TY or Tvis), desirable reflective coloration (e.g., desirable a* and b* reflective color values), low SF, low SHGC, and high LSG for a coated article in window applications. Note that as visible transmission increases parameters such as SF and SHGC may also increase, and En may decrease, with this being based on the desired transmission for instance of a given coated article for a given application. Coated articles according to certain example embodiments of this invention substantially reduce the red reflective color while retaining a low visible reflectance, while maintaining good mechanical, chemical and environmental durability and low emissivity properties.
In certain example embodiments of this invention, certain applications such as monolithic window applications desire reflective coloration that is not significantly red. In other words, certain applications such as monolithic window applications desire reflective a* color values that are either negative or no greater than +1.6 or +1.0 (glass side and/or film side reflective a* values higher than +1.6 are often considered too red). Such reflective a* values are desirable in the context of glass side reflective (RG[or outside, or exterior]Y) and/or film side reflective (RF[or inside]Y) a* values.
Certain embodiments of this invention relate to coated articles that include two or more functional infrared (IR) reflecting layers sandwiched between at least dielectric layers, and/or a method of making the same. The dielectric layers may be of or include silicon nitride or the like. In certain example embodiments, the IR reflecting layers are of or include titanium nitride (e.g., TiN). It has surprisingly and unexpectedly been found that the use of titanium nitride for the IR reflecting layers in a given solar control coating surprisingly results in improved emittance, SHGC and/or LSG values, and may be designed to surprisingly improve reflective a* values which are often desirable characteristics in window applications. Coatings according to embodiments of this invention may be designed so that before and/or after any optional heat treatment such as thermal tempering the coated articles realize one or more of: desirable glass side and/or film side reflective visible coloration that is not too red; a desirably low solar heat gain coefficient (SHGC); desirable visible transmission (TY or Tvis); thermal stability upon optional heat treatment (HT) such as thermal tempering; desirably low normal emissivity/emittance (En); and/or desirably high light-to-solar gain ratio (LSG). Such coated articles may be used in the context of monolithic windows, insulating glass (IG) window units, laminated windows, and/or other suitable applications for architectural or vehicle purposes.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer comprising silicon nitride; a first infrared (IR) reflecting layer comprising a nitride of titanium on the glass substrate over at least the first dielectric layer comprising silicon nitride; a second dielectric layer comprising silicon nitride on the glass substrate over at least the first dielectric layer comprising silicon nitride and the first IR reflecting layer comprising the nitride of titanium; a second layer IR reflecting layer comprising a nitride of titanium on the glass substrate over at least the second dielectric layer comprising silicon nitride; a third dielectric layer comprising silicon nitride on the glass substrate over at least the second IR reflecting layer comprising the nitride of titanium; wherein the coating contains no IR reflecting layer based on silver; and wherein the coated article measured monolithically has: a visible transmission from about 12-70%, a glass side visible reflectance no greater than about 16%, and a glass side reflective a* value of from −10 to +1.6.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer; a first infrared (IR) reflecting layer comprising a nitride of titanium on the glass substrate over at least the first dielectric layer; a second dielectric layer comprising silicon nitride on the glass substrate over at least the first dielectric layer and the first IR reflecting layer comprising the nitride of titanium; a second layer IR reflecting layer comprising a nitride of titanium on the glass substrate over at least the second dielectric layer comprising silicon nitride; a third dielectric layer on the glass substrate over at least the second IR reflecting layer comprising the nitride of titanium; wherein the coating contains no IR reflecting layer based on silver; and wherein the coated article measured monolithically has: a visible transmission from about 12-70%, a glass side visible reflectance no greater than about 16%, and a glass side reflective a* value of from −10 to +1.6.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer comprising silicon nitride; a first infrared (IR) reflecting layer comprising a nitride of titanium on the glass substrate over at least the first dielectric layer comprising silicon nitride; a second dielectric layer comprising silicon nitride on the glass substrate over at least the first dielectric layer comprising silicon nitride and the first IR reflecting layer comprising the nitride of titanium; a second layer IR reflecting layer comprising a nitride of titanium on the glass substrate over at least the second dielectric layer comprising silicon nitride; a third dielectric layer comprising silicon nitride on the glass substrate over at least the second IR reflecting layer comprising the nitride of titanium; wherein the coating contains no IR reflecting layer based on silver; and wherein the coated article measured monolithically has a visible transmission from about 12-70% and one or more of: (a) a glass side visible reflectance no greater than about 16%, (b) a glass side reflective a* value of from −10 to +1.6, (c) a film side visible reflectance no greater than about 16%, and (d) a film side reflective a* color value of from −8 to +1.6.
In certain example embodiments of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer comprising silicon nitride; a first infrared (IR) reflecting layer comprising a nitride of titanium on the glass substrate over at least the first dielectric layer comprising silicon nitride; a second dielectric layer comprising silicon nitride on the glass substrate over at least the first dielectric layer comprising silicon nitride and the first IR reflecting layer comprising the nitride of titanium; wherein the coating contains no IR reflecting layer based on silver; and wherein the coated article measured monolithically has: a visible transmission from about 12-70%, an LSG of at least 1.00, and a glass side reflective a* value of from −10 to +1.6.
Thus, this invention covers monolithic window units, IG window units, laminated window units, and any other article including a glass substrate having a coating thereon as claimed. Note that monolithic measurements may be taken by removing a coated substrate from an IG window unit and/or laminated window unit, and then performing monolithic measurements. It is also noted that for a given coating the SF and SHGC values will be significantly higher for a monolithic window unit than for an IG window unit with the same coated article.